Terminological barriers, examples of fastener selection pathways
How to efficiently determine the "correct" fastener type for components or components involving composite and plastic materials? To define which materials and concepts are applicable to fastener types, it is necessary to understand the materials involved, their forming process, and the required connection or assembly functions.
Taking the internal panel of an aircraft as an example. Simply describing it as an "aerospace composite material" oversimplifies the rich available materials and processes. Similarly, the term "aviation fasteners" lacks specificity in terms of the most suitable materials for fasteners and their functionality. Fasteners, such as insert studs, rivet studs, surface bonded fasteners, and welded fasteners, may all be suitable for aerospace applications, but there are significant differences in the materials and functions they can be tightened with.
The problem of searching in the fastener world is how to classify fastener products, usually using terms specifically related to fasteners rather than the materials they are most suitable for. However, composite material specific terms often have limited relevance when browsing fastener categories. For example, without a detailed understanding of surface bonding or ultrasonic welding in fastener installation, how do you know if surface bonding or ultrasonic welding fasteners are suitable fastening options for hot formed laminated materials? If your world is about polymer matrix properties, fiber reinforced structures, and processing parameters, how do you search and choose in a world that discusses assembly strategies, tightening directions, tightening torque expectations, and target preloads?
Contacting fastener suppliers or distributors for advice and guidance is usually an effective and successful first step; However, by presenting the application in a way that allows for simple and quick search of relevant options, further simplification can be achieved. Here, we take the thermoplastic aircraft inner panel as an example to illustrate the important aspects of this approach to improving fastener selection.
Tightening requirements
Firstly, defining fastening requirements is helpful. Do you want to create a fastening point for composite materials or plastic components to prepare for subsequent assembly operations? Or, do you want to directly fix the component to composite materials or plastic components or fix it to them?
For our example, the requirement is to create fastening points - especially providing threaded connection points on composite panels. Therefore, we will shift towards technology that provides methods for installing and fastening connection points, rather than technology used to directly fix components together. It is relatively easy to classify fastening techniques using these terms, and the terms are relatively simple, so everyone can communicate in the same language.
Material concept
The factors related to the materials involved may affect the applicability of fastener types, but the relevance of these factors usually depends on the type of fastener being considered. To break this cycle and avoid overly detailed dialogue during the early filtration process, we can generally define composite materials and plastic materials as:
No reinforced polymer.
Discontinuous fiber reinforced polymer materials.
Continuous fiber reinforced polymer laminates.
Sandwich material.
Non woven and fiber materials.
In our example, the internal panel material of the aircraft is a continuous fiber-reinforced polymer in a laminated structure. By defining material concepts in this simple way, we can quickly focus on a series of related material considerations:
How will fasteners be integrated into the manufacturing process chain?
How do materials affect fastening integration or installation?
For example, integrating fasteners into continuous reinforcement materials before or during hot forming may result in unwanted process complexity, such as cutting or shifting fibers, which may have an undesirable impact on mechanical properties. In other words, continuous fiber reinforcement may pose challenges to the integration of co processed fasteners, and people may want to avoid such challenges.
At the same time, it only requires a basic understanding of fastening technology to determine whether it is to use co process installation or post process installation. By simplifying material and fastening terminology, it is possible to quickly and easily see which matches and which do not match. In our example, the selection of fasteners should focus on post-processing techniques, unless we wish to integrate fasteners into continuous fiber reinforced materials/manufacturing processes.
Detailed requirements
At this point, in order to determine the relevant fastening techniques, we need to define more details about the fastening strategy, materials involved, and forming process. For our example of continuous fiber-reinforced laminates, we will define the application as follows:
The general application is the internal side panels of aircraft.
The fastening strategy is to provide a double headed bolt on the back of the panel (not visible) for connecting the polymer window area with a nut.
The fastening requirement is a blind, invisible external threaded connection point - blind means installation/fastening from one side of the component - capable of withstanding a pull-out force of approximately 500 Newtons.
Panel is a continuous fiber reinforced thermoplastic material, and the installation of fasteners must be carried out after the molding process to avoid damaging the reinforced structure.
Further sort the factors and select downwards
Looking at our example, we can start to see that multiple factors can influence our decision on which type of fastener to use. The question is, which of these factors is most important, especially if fastener cost is not the only decisive factor? In our example, we will narrow down the selection range to surface bonded fasteners or ultrasonic welded fasteners.
Here, even simple application information can be helpful. For example, knowing that we are using thermoplastic materials helps us set relevant performance expectations. Considering the availability of professional adhesives and surface treatment technologies, we can expect the mechanical performance of both technologies to reach a reasonable level.
However, because we know that the application is in aerospace, mechanical interlocking connections can provide simpler performance guarantees and certification pathways. Adhesive takes time to cure, while ultrasonic installation can immediately load, so we should consider the impact of process time. Access restrictions may also be a key factor. Although inner panels are often easily provided for fastener installation with automatic adhesive applicators or ultrasonic machines, they should be carefully inspected before final selection.
Make the final decision
It is impossible to make decisions solely based on connection method identification and fixed time; The final decision will depend on considerations of equipment investment, mechanical performance and durability, overall process time impact, access restrictions, and approval or certification strategies. In addition, design, manufacturing, and assembly operations may involve different stakeholders, so the final decision requires their participation. In addition, making this decision requires considering the entire value proposition, including productivity and total cost of ownership (TCO - total cost of ownership). By taking a holistic view of fastening issues and considering all relevant factors during the initial design phase, manufacturing process, and final assembly operations, productivity and TCO can be calculated and positively impacted. These are one of the key principles of the Bossard assembly technology expert education portal, aimed at helping individuals acquire assembly technology knowledge.
Ultimately, the decision on which tightening strategy or product to use depends on multiple factors - there is no one size fits all solution, and there are many different choices to consider. However, as we have outlined above, even defining application details in a relatively simple way can simplify the selection process, highlight relevant decision-making factors, and identify areas that may require stakeholder input.
Post time: Feb-06-2024
